The long term goal of this project is to determine the mechanism of recombination of virus DNA with the host chromosome. Recombination between virus and host involves specialized regions in each DNA called attachment sites. The locus of crossing-over lies within the attachment sites, specifically in a 15 bp region of homology called the core. Where within the core does polynucleotide strand breakage and rejoining actually occur? In collaboration with A. Landy, we have found that such breakage and rejoining can occur at two core positions (between bases -2 and 0, and between bases 4 and 5, where position 0 is the core center). We are further analyzing the function of the virus attachment site by isolation and sequencing of point mutations. Our initial results suggest that many of the bases within the attachment site can be changed without affecting site function. We are continuing our analysis of a virus mutant that increases the activity of integrase, the enzyme that promotes virus-host recomeination. Our results suggest that the mutation is located upstream of the DNA region that encodes tha protein and may therefore act to increase the amount of the enzyme.